In a study published in journal Cell Reports scientists have described how they have used super-resolution microscopy to not only capture stunning images of what interior of cells, detailing not only the cell’s internal organs and skeleton, but also providing insights into cells’ amazing flexibility.
Researchers used the super-resolution microscopy to provide a sharp view of the geodesic mesh that supports the outer membrane of a red blood cell, revealing why such cells are sturdy yet flexible enough to squeeze through narrow capillaries as they carry oxygen to our tissues.
If we look at typical human cells, they have a two-dimensional skeleton that supports the outer membrane and a three-dimensional interior skeleton that supports all the organelles inside and serves as a transportation system throughout the cell.
Red blood cells, however, have only the membrane supports and no internal scaffolding, so they’re basically a balloon filled with molecules of oxygen-carrying hemoglobin. Because of their simpler structure, red blood cells are ideal for studying the skeleton that supports the membrane in all cells.
Electron microscope images earlier showed that the sub-membrane cytoskeleton in red blood cells is a triangular mesh of proteins, reminiscent of a geodesic dome. But measurements of the size of the triangular subunits were made by flattening out the domed membrane of a dead and dried-out cell, which distorts the structures.
The distinction is critical: The building blocks of the mesh are a protein called spectrin, which can be stretched to a maximum of about 190 nanometers in length. If the mesh were made of stretched spectrin, it would be rigid, researchers explain. But since its normal length is a relaxed 80 nanometers, it acts like a spring.
At the vertices of the mesh, where five to six spectrin proteins come together, is a different protein: actin. Actin is a standard part of the sub-membrane cytoskeleton and one of the main structural components of the cell.
Super-resolution microscopy employs a trick to overcome the diffraction limit of light microscopy, which prevents conventional light microscopes from resolving things smaller than half the size of the wavelength of the light, which for visible light is about 300 nanometers.